Has anyone got enough flight time on their GO25 to wear it out? Just wondering if you think it lasted long enough. I just took mine apart after allot of bench and flight testing on 1/2 castor/synthetic blend and yeah buddy it's shot. The last session it was pumping out black oil. The big end was loose and the rod was rubbing on the case. Aluminum slurry all through the motor. The piston wore through the chrome around the exhaust port, never seen that before, can't even get it re-pinched. Wrist pin hole in the piston was allot bigger. Bearing races were frosted and the front one was slightly spalled. Not sure they're using the best ball bearings or bushing material in the rod and I'm sure the chrome's not very thick. Anyway, I'm switching brands but going to re-build it for a practice mule. No association but if anyone needs GO Pro25 parts or engines call Rich 425-208-2655.

MM

How do you make an engine that gets better protection on synthetic than castor?

I usually run all castor but in some hotter running engines it turns the piston black but never seen one slow down with a black piston. Castor still lubes even after it burns.

A truggy motor has lots of cooling and it's on suction so heat hasn't been a problem. Just the opposite I've been reducing head fins and increasing compression ratio to keep it lit. The only residue I've seen is very little on the top of the piston near the exhaust port and this is from break in to worn out.

I only tried 1/2 and 1/2 because that's the swill they use at the nats. I'm going to 15 castor 5 synthetic.

My point was I think GO is poorly made compared to the major brands. The guys I know that run them have 3-4 spare motors and parts ready.

MM  

IDK, I guess for $160 I got my fun out of it. Usually when a piston/sleeve wears out you can rebuild and sometimes use the same rod. This engine got a little loose on the big end and started rubbing the case which ruined the crank too. Crank pin is .005" out of round. The new rods have a channel cut around the big end to relieve oil drag they are fitted that close. All I'm saying is, if you have the tools, cut some more clearance for the rod in the crankcase and maybe you can save the crank when you rebuild.

Also, It tells you in the manual to put in a new rod after break in. It might be worth pulling the back plate to have a look.

The case is the only useable part left but, to be honest the crankcase didn't need too many mods so, instead of rebuilding, it would better/cheaper to just use it until it goes south then swap the burn room, venturi, drive washer ect to a whole new engine.


MM

OK, got the Go25 Sport (car version) apart and it has a few differences.

Crank has a big tang on the crank pin for a starter which has to be cut off. The back plate has a big circular cut out for the pin so the back plate is useless. The PTO shaft has a cross hole, don't like it. I don't know if this is on the Pro shaft as I've only seen the marine shaft which doesn't have the hole. The turbo swirl is there but the knife edge cut on the left side of the crank web is missing. I'm going to leave it to see how it balances. The pro25 has a bad vibration in the low 20's.

The rod is the same except it's not knife edged. A little work with a file will make it a Pro rod. I'll probably just use it as my break in rod.

The sleeve has 2 side ports and one boost port, no finger ports and no under piston port or port holes in the piston. The exhaust port is the same size but doesn't have all the angles cut into it. Might be good for a beater motor.

I have a new 6 port sleeve to use in the build. It had allot of flashing on all edges of the porting that had to be painstakingly removed under magnification with the smallest diamond cutter I had since it was chromed flashing.

If you don't like dremel tool work don't get this engine. The crankcase is the same casting but they skipped some key mill work to save time. The cut outs on the sides of the lower boost transfer are not there and the cut outs in the exhaust passage where not done. I used a 1/8th straight cutter for the exhaust and a 3/8ths ball for the boost. I cut more relief for the rod as mentioned before. Increased the diameter by .020" and widened it .005" front and back on the lathe. This leaves .045" wall thickness in that area. I took .010 off the top of the case for better head fin clearance. Blended the sharp corners in the intake area. It has the groove between the intake port and front bearing but it's not connected to the intake port. I don't think it needs this with a sealed front bearing. btw the front bearing had both rubber seals left on also to save time I guess geez.

More later.

MM

Got it all together and noticed the liner seems to be sitting higher in the case than on the Pro25. I'll have to put the degree wheel on it later. I took the OEM turbo burn room (special order) and made a few mods then cut the gasket area down for a .010" piston clearance.

Piston fit was way too tight. Forced it through TDC then took the head off to find black oil. Cleaned it up and took it out to the test stand and hit it with a propane torch. Helped enough to flip it but it was still really tight, had a hard time getting it started. Finally got it running and set it for a slightly rich 20K and ran 2 oz through it. After that I can flip it ok but still locks up when you pull it through slow.

Half way through the next tank I couldn't resist and pinched the fuel line down and man it went there. It's still too tight to race but already turning the same rpm as my good engine did in it's prime. Looks like the Sport 25 is no slouch after mods.

MM